INTERNAL COMPARTMENTATION OF RAT-LIVER MITOCHONDRIA - TOMOGRAPHIC STUDY USING THE HIGH-VOLTAGE TRANSMISSION ELECTRON-MICROSCOPE

The three-dimensional organization of the internal compartments of con ventionally fixed and embedded rat-liver mitochondria has been determi ned by tomographic reconstruction from tilt-series images collected on the Albany high-voltage electron microscope. The results indicate tha t the inner membranes of these organelles are predominantly tubular in the orthodox (expanded matrix) conformation, as previously suggested by scanning electron microscopy. In the condensed (contracted matrix) conformation, the intracristal space opens up into large irregularly s haped compartments which are connected to each other and to the extern al (intermembrane) space by tubes with approximately the same diameter (20 nn) as those observed in the orthodox state. These results raise several questions, in particular about the nature of the structural tr ansitions that occur in the cristae during matrix expansion and contra ction, and about the influence of inner-membrane shape on the diffusio n of ions and metabolites between the intracristal and intermembrane c ompartments.